This invention relates to a unique method and apparatus for correcting drive wheel slippage in a vehicle.
A typical configuration for a heavy vehicle includes a front non-drive axle with two non-driven wheels and either a single or tandem rear drive axle. A single rear drive axle includes first and second driven wheels which are rotated by a driveshaft through a main differential. A tandem rear drive axle includes a front drive axle with a first pair of driven wheels and a rear drive axle with a second pair of driven wheels. The front and rear drive axles are interconnected by an inter-axle differential which transfers rotation and torque from the front drive axle's main differential to the rear drive axle's main differential. Under poor traction conditions, such as mud or ice, all of the driving power or torque may be transferred to a single driven wheel. When this single driven wheel is on a slippery surface, the wheel will spin in one place while all of the remaining driven wheels are motionless. This condition is known as wheel slip and is undesirable because it prevents the vehicle from moving in a forward or reverse direction.
To avoid wheel slip, the main differentials include a locking mode which locks the driven wheels together, forcing them to be driven at the same speed and thus preventing all of the driving power from being transferred to any one wheel. In a tandem configuration, the inter-axle differential also includes a locking mode which locks the front and rear drive axles together, forcing them to be driven at the same speed. When using differentials with locking modes, it is important to set certain conditions under which the differentials should be locked. Some systems require the driver to control when the differentials are locked while other systems are electronically controlled.
Current systems for correcting drive wheel slippage include sensors located at each driven wheel for measuring the driven wheel speeds. A central processor monitors driven wheel speeds to determine if there is drive wheel slip. Once slip is detected either the inter-axle differential, main differentials, or some combination thereof are locked. Additional sensors may be located at the non-driven wheels to measure the non-driven wheel speeds. When non-driven wheel sensors are used, the central processor monitors both the measured driven and non-driven wheel speeds to determine if there is drive wheel slippage. Thus, in order for current systems to be operable, at least all driven wheels are monitored with an associated speed sensor.
It would be desirable to reduce the number of sensors on the driven wheels. Current systems which require sensors located at each of four driven wheels to determine if there is slippage are undesirably complex. Thus, there is a need for a system for correcting drive wheel slippage which does not need any input from driven wheel sensors. Also, the system must be easily adapted to current systems and must have the flexibility to be used on any and all vehicle configurations.